Ovens for cooking food and wood fired ovens in particular are ancient in origin. Although high technology gas and electric ovens are now available, many people regard wood fired ovens as capable of providing preferred flavours to foods. There has therefore always been a demand for wood fired ovens. Relatively recently this demand has undergone something of resurgence for preparation of food, particularly foods such as pizzas, tandoori style meals and roasts. Typically, a modern wood fired cooking oven will be formed with a flat base of refractory material and a dome of refractory material forming an enclosure in which a solid fuel may be burnt while resting directly on the base. The burning fuel shares the floor space with food to be cooked. Various portholes may be provided to facilitate access for food and fuel as well as for the discharge of hot gases. The latter are often channelled through flues. The dome is usually formed by casting a hemisphere of refractory material which may be cast in situ or alternatively cast such as in a factory elsewhere and transported to the final assembly point.
As noted, the material used in formation of the ovens is described as “refractory” which includes the notion of a material having the ability to retain its physical shape and chemical identity when subject to high temperature. Typically, the refractory material is formed as bricks of various shapes and sizes used for lining a furnace or oven.
Once the oven inner structure is formed, a surround is subsequently built around the oven to enhance insulation and minimise the chance of damage to surrounding structures and people operating the oven.
A limitation of this approach is that the dome must be self-supporting. As a result, the size and shape of the dome is somewhat limited. Further, the refractory material is relatively brittle which presents a problem when attempting to mould the dome in one piece at a ceramic factory and transport it undamaged to the oven site without cracking.
The need for strength also favours the production of predominantly hemispherical domes which result in a central high point of the oven. The roof of the oven contributes to the cooking process as it acts as both a restraint on heat loss and a reflector or radiator of incident heat on to material to be cooked. Efficiency of the oven is enhanced if the roof is kept as close as possible to the food to be cooked, thereby maximising both concentration and reflection of the heat. While it is possible to vary the shape of the dome by having a lowered central region, this approach leads to weaknesses which may result in substantial reduction of oven working life and even catastrophic failure.
A further problem inherent with the prior art ovens is the limitation on the number of portholes that may be included for accessory features. Each aperture in the dome creates a weak point. It is generally preferred to minimise the number of such apertures to an access port for loading fuel and food which may also serve as an exit port for hot gases. Various other apertures may be of considerable use such as those provided for lighting, viewing windows, char-grilles, fire retardant systems, extra doors and gas fire systems. These additional useful access ports are therefore traditionally avoided if possible.
Various responses to the challenge of forming an oven dome have been documented. U.S. Pat. No. 4,108,138 to Petin and Richardson discloses a method of forming a dome by casting hemispherical sectors of refractory material and assembling the sectors into a dome while supported by a base. The sectors are formed with interlocking edges to help hold them together and the entire dome is enclosed within an insulated chamber. While this innovative approach overcomes some of the problems of providing an oven dome, it still encounters the problem of relatively weak structural integrity thereby minimising the ability to provide extra or multiple apertures in the oven. Further it has been found that expansion and contraction during heating cycles leads to wear in the interlocking edges with resultant weak points in the oven walls.
U.S. Pat. No. 4,474,165 to Richardson describes an improved cooking oven which has two flat surfaces covered by an enclosure. Three openings are provided in the wall of the enclosure, two of which are used for passage of food and fuel while the third serves as a flue. This oven is built in a similar fashion to that described in U.S. Pat. No. 4,108,138 referred to above. Surrounding the dome is an outer wall of brick or other suitable structural material. Insulating material is placed in the space between the outer surface of the dome and the inner surfaces of the wall and the cover. The insulating material may include a ceramic fibre blanket directly over the dome. Further insulating material is provided in the form of vermiculite for example, to fill the space between the blanket and the wall beneath the cover. The sectors are formed from a refractory known as “Moldit D”™ with metal fibres dispersed therein. The sectors are moulded separately and then brought in finished form to the oven construction site to be assembled. Thus, the more difficult task of moulding the dome in one piece and then transporting it to the oven site without cracking it is avoided. This invention is a variation on that referred to in the earlier US patent and one inventor is common to both. It suffers from the same problems described above.
U.S. Pat. No. 5,413,033 to Riccio discloses an oven with a stone covered bottom. The stone covered bottom includes a baking area in which the food product is baked. The top of the oven is connected to the bottom and constructed to form a domed chamber over the baking area. The top is constructed from a plurality of pieces that are shaped to provide a conventional dome configuration. Each piece is constructed to permit expansion and contraction of the pieces caused by heat changes while preventing a piece from falling onto the bottom. It has been found that each piece is best formed with a tongue and groove configuration. This joint however, is prone to wear with resulting risk of shortening the working life. The issues of brittleness and risk in transport also arise.
European Patent No. 0409758 to Georges and Tisserant describes a wood burning oven with a high throughput rate. The oven is constituted by a roof made of refractory materials of annular shape, concave in its centre and with a rotating floor. The oven is particularly suitable for rapid cooking dishes such as pizzas.
The prior art does not described a method of producing a top section for an oven which may be formed in a factory and transported safely and relatively easily to the assembly point and wherein the top section also has considerable structural strength.